Dragonflies move
like ballet dancers when they hunt, according to new research by
entomologists from the University of Arizona, Howard Hughes Medical
Institute, and Union College in Schenectady, NY.
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The
Blue dasher, female, photographed in Skaneateles, NY. Image
credit: R.A. Nonenmacher / CC BY-SA 3.0.
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"Dragonflies
on the hunt perform internal calculations every bit as complex as
those of a ballet dancer," said Dr Anthony Leonardo of Howard Hughes
Medical Institute, who is the senior author of a paper
published in the journal Nature.
Dr Leonardo and his collaborators spent several years devising
a system that allows them to track a dragonfly's body movements
as it intercepts its prey.
Their approach is based on the same technology used to translate
the movements of actors into computer animation. Using the position
of each flash of light, the team can reconstruct an outline of the
dragonfly as it flies.
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Common
Whitetail - Adult Male
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Common
Whitetail - Adult Female
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The scientists filmed the movements of common
whitetails (Plathemis lydia) as they chased after either a fruit
fly or an artificial prey a bead maneuvered by a pulley system
whose movements they could precisely control. They focused
on following the orientation of the dragonfly's head and body.
When the researchers analyzed their videos, it was clear that the
dragonflies were not simply responding to the movements of the prey.
Instead, they made structured turns that adjusted the orientation
of their bodies even when their prey's trajectory did not
change.
"Those turns were driven by the dragonfly's internal representation
of its body and the knowledge that it has to rotate its body and
line it up to the prey's flight path in a particular way," Dr Leonardo
said.
Dragonflies
always aligned themselves so that they would intercept their prey
from below, reducing the risk of detection.
"At the end of the chase, the fly makes a basket out its legs and
the prey drops into it," Dr Leonardo said.
Those shifts in orientation create a challenge for the predator.
The scientists found that each dragonfly moved its head to keep
the image of its prey centered on the eye, despite the rotation
of its own body.
The head movements happened too fast to be a reaction to visual
disturbances created by the rotation of the dragonfly's body. Instead,
the head movements must be planned based on the insect's predictions
about how to stabilize the image of its prey.
"The movements we observed are so fine-tuned that they keep the
image of the prey fixed in the crosshairs of the dragonfly's eyes
their area of greatest acuity during the duration
of the chase. That allows the dragonfly to receive two channels
of information about its prey," Dr Leonardo said.
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